The concept of home incarceration has evolved as an alternative to detention in government jail and prison facilities. In cases of relatively light infractions, offenders, rather than being placed as inmates in overcrowded facilities, are confined to predetermined limited geographical areas including, for example, homes and workplaces. The burden on the prison system is relieved by enabling more space for criminals convicted of more serious crimes. Cost efficiency is also a significant factor as the expense of incarceration in such a facility is quite high. The degree of severity of punishment and the prospects of rehabilitation of the light offender are more appropriate to a home incarceration environment than in a prison provided for felons.
In a "house arrest" situation, the detainees, of course, are more likely to interact with the community. Public security is a socially sensitive issue and it is important that the activities of captives be monitored and supervised. The whereabouts and identity of individuals should be capable of being established at any time without the necessity of assignment of a law enforcement officer for constant surveillance on a one to one basis.
A prior art monitoring arrangement is shown in FIG. 1. A bracelet 20 is worn on the wrist or ankle of the detainee. A radio transmitter 22 broadcasts a coded signal which is received at a base 24. The base may be stationary or mobile. Verification of the received coded signal is performed at the base as indicated in block 26. Inasmuch as the signal has a limited range, reception of the signal at the base is indicative that the bracelet, and presumably the detainee, is within the defined area of confinement. The signal may be continuously or selectively generated.
The base is under the control of a processor through a telephone line 30. The processor may be part of a local area network including a file server 32 having data base information of all detainees in the system. At any time the system may call, via the telephone, the confinement site and ask for verification. Telephone calls may be made randomly or at scheduled intervals determined by the system. If the signal is to be continuous and the base senses an interruption in the signal, the system will initiate a call for verification.
During a call, the detainee is requested to position the bracelet appropriately near the transmitter. The transmitter then picks up the code from the bracelet and transmits it back to the base. If the transmitter is beyond the range of the base, or if the code is not verified, the base can initiate a call to the system processor to indicate that the detainee is not responding or has not been verified.
A similar prior art arrangement is disclosed in U.S. Pat. No. 4,747,120. A bracelet capable of generating a coded signal is worn by the person to be monitored. A decoder, connected with a telephone, can decode the signal when the bracelet is appropriately positioned adjacent the decoder and the decoded signal can be transmitted over the telephone network to the remote system.
The above described arrangements, intended for selective or continuous personnel monitoring, have inherent disadvantages. In the prior art embodiment of FIG. 1, lengthy interruptions in signal transmission can be caused by various sources of interference. As a result, the base may give frequent false indications of nonverification, requiring human intervention. Where the coded signal is transmitted by the phone line, rather than by radio transmission, continuous monitoring is impractical, as an on line connection must be continuously maintained for each person monitored.
A phone call by the system to the confinement site for purposes of verification will not be productive during periods in which radio transmission is interrupted by interference. As a backup for such instances, monitoring personnel may attempt to identify the voice of the called party during the telephone conversation. The listener would be required either to know the confinee personally or be familiar with voice recordings of the individual to be verified. Such identification attempts likely would not be successful if the system serves a large number of detainees or if the speech of the called party is slurred by the influence of drug or alcohol abuse. Enforcement personnel frequently must be dispatched to the confinement sites to resolve the issue.
A further drawback of these systems is that the coded signal may be verified without complete assurance that the signal emanates from the location of confinement. In the case of radio transmission to the base, while the transmission range may be limited, the range may nevertheless extend beyond the bounds of confinement. In the case of telephone transmission, the system may be thwarted by placement of a decoder at a telephone, which is provided with call forward service, in an unauthorized area. A call placed by the system to the site of incarceration could be call forwarded to the unauthorized area and the code would be verified, falsely indicating that the detainee is identified and present at the appropriate location.
A further complication in these systems involves the physical structure of the bracelet. Bracelets must be constructed to resist tampering. The device must be affixed to the particular individual so that the identity of that person can be assured when receiving the signal transmission. The device is cumbersome in order to prevent easy removal. In addition, each bracelet must have a self-contained power supply sufficient for operation over an extended time period.
U.S. Pat. No. 4,843,377 contemplates the use of a voiceprint as a means for remote identification of a prisoner. Audio spectral analysis is performed and applied to speech transmitted over a telephone line to determine a match with a probationer's voiceprint. Several commercially available systems are discussed.
While voice analysis may be a reliable means to determine the identity of an individual, such a system, in itself, cannot verify that the individual is at the prescribed location. Call forwarding, in the network or on the premises, can result in the appearance of a party being in the prescribed location, while in fact, being elsewhere.